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python3/modbus_client_sim.py

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+import socket
+import struct
+import time
+
+# 配置信息
+SERVER_IP = '127.0.0.1'  # 模拟本地回路
+PORT = 502
+UNIT_ID = 1
+REG_ADDR = 30  # 逻辑 40031
+
+def poll_register():
+    # 1. 构造 Modbus TCP 请求 (Function Code 03)
+    tid = 0x0001
+    pid = 0x0000
+    length = 6 # 后续字节长度 (UnitID 1 + PDU 5)
+    uid = UNIT_ID
+    
+    fc = 0x03
+    addr = REG_ADDR
+    qty = 1
+    
+    # [MBAP Header] + [PDU]
+    request = struct.pack('>HHHB', tid, pid, length, uid) + \
+              struct.pack('>BHH', fc, addr, qty)
+              
+    try:
+        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+            s.settimeout(2.0)
+            s.connect((SERVER_IP, PORT))
+            print(f"[TX] 发送请求: {request.hex(' ')}")
+            s.sendall(request)
+            
+            # 2. 接收响应
+            response = s.recv(1024)
+            if not response:
+                print("[!] 服务器关闭了连接")
+                return
+
+            print(f"[RX] 收到响应: {response.hex(' ')}")
+            
+            if len(response) >= 9: # MBAP(7) + FC(1) + ByteCount(1)
+                # 解析响应
+                header = response[:7]
+                pdu = response[7:]
+                
+                res_tid, res_pid, res_len, res_uid = struct.unpack('>HHHB', header)
+                res_fc = pdu[0]
+                byte_count = pdu[1]
+                reg_value = struct.unpack('>H', pdu[2:4])[0]
+                
+                print(f"[+] 解析成功!")
+                print(f"    - 事务ID: {res_tid}")
+                print(f"    - 寄存器 {REG_ADDR} 的值: {hex(reg_value)} ({reg_value})")
+            else:
+                print("[!] 响应长度不足")
+                
+    except Exception as e:
+        print(f"[!] 连接错误: {e}")
+
+if __name__ == "__main__":
+    print("[*] Python Modbus TCP 客户端模拟启动...")
+    poll_register()